**Question:** In a patient with suspected tubercular anterior uveitis the diagnosis is confirmed by:

A. Chest X-ray
B. Mycobacterial culture
C. Tuberculin skin test (TST)
D. Fiberoptic anterior chamber paracentesis (FACP)

**Correct Answer:** D. Fiberoptic anterior chamber paracentesis (FACP)

**Core Concept:**
Anterior uveitis is a type of inflammation affecting the anterior segment of the eye, including the iris and ciliary body. In infectious etiologies, tuberculosis (TB) is a common cause, especially in endemic regions. Diagnosis of tubercular anterior uveitis requires specific tests to confirm the presence of Mycobacterium tuberculosis and its associated immunological response.

**Why the Correct Answer is Right:**
Fiberoptic anterior chamber paracentesis (FACP) is the correct answer because it provides direct evidence of M. tuberculosis and its associated immune response in the affected eye. This procedure involves using a fiberoptic instrument to collect a small sample of aqueous humor from the anterior chamber of the eye for laboratory analysis. FACP allows for the isolation of M. tuberculosis and detection of specific immunological markers, such as the presence of M. tuberculosis DNA and the release of interferon-gamma (IFN-γ) during a tuberculin skin test (TST), which indicates a specific immune response to M. tuberculosis.

**Why Each Wrong Option is Incorrect:**

A. Chest X-ray (CXR) is an important tool for diagnosing extrapulmonary TB; however, it is insufficient for confirming the diagnosis of anterior uveitis. CXR might show suggestive findings, but it is not specific for the diagnosis of TB in uveitis patients.

B. Mycobacterial culture is essential for diagnosing TB, but it is not specific for anterior uveitis. A positive culture result from a non-inflammatory site (e.g., sputum or lymph node aspirate) confirms the presence of M. tuberculosis, but a positive culture from an inflammatory site cannot confirm the diagnosis of anterior uveitis.

C. Tuberculin skin test (TST) is an indirect method that measures the patient's immune response to M. tuberculosis. While it indicates an immune response to TB, it does not directly confirm the presence of M. tuberculosis in the affected eye.

**Clinical Pearl:**
When faced with a patient presenting with suspected tubercular uveitis, FACP is the definitive test for diagnosing the presence of M. tuberculosis and assessing the specific immune response to the bacteria. Combining FACP with TST and CXR can provide a comprehensive evaluation for tubercular uveitis. However, TST and CXR alone are insufficient for confirming the diagnosis of anterior uveitis.